JPH0645694A - Top emission-type vcsel provided with injected substance - Google Patents

Abstract

PURPOSE: To provide a top emission type VCSEL which is newly improved by a simple manufacture, and enable large output power and high efficiency. CONSTITUTION: This VCSEL contains a central active layer 16, having an upper mirror lamination part 18 and a lower mirror laminating part 14. A circular trench 20 is formed in the mirror laminating part 18 and defines a laser irradiation region 25. The trench 20 decreases reflectivity and prevents laser irradiation outside the operating region 25. Deep beryllium injection material 27 in the mirror laminating part 14 or the mirror laminating part 18 restricts current distribution, together with the trench 20. Thereby power output and efficiency are maximized. In an example, transparent metal contact is used as a top contact.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to vertical cavity surface emitting lasers (VCSELs). More specifically, top emit with higher power and greater efficiency.
ting) VCSEL.

[0002]

2. Description of the Related Art Recently, there has been an increasing interest in a new type of laser device called a vertical cavity surface emitting laser (VCSEL). The advantages of VCSEL devices are that they are smaller, have the potential to have higher performance, and may be more productive. These advantages are due, in part, to the development of epitaxial deposition techniques such as metal organic vapor phase epitaxy (MOVPE) and molecular beam epitaxy (MBE).

However, with these advances in deposition technology, it is difficult to control the mode of operation of the laser during manufacture and to control the current distribution within the laser. Generally, a VCSEL is created by depositing multiple layers on a substrate and then etching the layers down to the depth of the substrate that will form the VCSEL. For example, US Pat. No. 5,034,092 “Plasma Etching of Semicon,” which was assigned to the same assignee as the subject matter of July 23, 1991 and is also incorporated herein by reference.
See ductor Substrates ”.

Etching the mesas to make a VCSEL has two drawbacks. The etching process damages the surface crystals, which increases the threshold current,
It is less reliable. The mesas form a waveguide with a large discontinuity in the index of refraction, which makes it difficult to control the optical modes without making very small devices, which increases series resistance and Reduce output power. In general, this results in less efficient and less stable devices.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a new and improved top emitting VCSEL which is easier to manufacture.

Another object of the present invention is to provide a new and improved top emitting VCSEL that produces higher output power and has higher efficiency.

First and second layers deposited on both sides of the active layer
The above and other problems are solved and the objectives achieved by a method of making a top-emitting VCSEL that includes a mirror stack of. The method comprises the steps of defining an emission region in the second mirror stack, etching the second mirror stack to form a trench surrounding the emission region, and extending the depth of the trench sufficiently. , A step of reducing the reflectivity below the amount required to accommodate laser irradiation in a non-laser irradiated volume of the laser between the trench and the active layer, and one of the first and second mirror stacks. Implanting impurities into the two non-laser-irradiated volumes to form an implant volume having a conductivity type different than one of the first and second stacks in which the implant was formed; Forming the implant volume to define a laser irradiation volume that is axially aligned.

Further, a top-emitting VCSEL solves the above and other problems and achieves the objectives. The VCSEL has an active area with opposing major surfaces and 1
A first mirror stack on one major surface and a second mirror stack on the other major surface, at least a portion of the second mirror stack having a generally circular cross section; An axis that is substantially perpendicular to the first and second mirror stacks is formed, and the mesa defines a laser irradiation volume that is generally axially aligned therewith, and further comprises a first and second mirror stacks. One of the impurity implants forms an implant volume having a conductivity type different from one of the first and second stacks in which the implant is formed, the implant volume being the laser irradiation volume. It is formed to be generally axially aligned and define a current path that is substantially coextensive with the laser irradiation volume.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In particular, FIG. 1 shows an intermediate structure in cross-section in the manufacture of a top emitting vertical cavity surface emitting laser (VCSEL) 10. The laser 10 is formed on the substrate 12,
This substrate is made of p-type doped gallium arsenide in this example. By depositing alternating layers of n-doped aluminum gallium arsenide (or aluminum gallium arsenide with different aluminum mole fractions) and aluminum arsenide, a reflector or mirror for laser 10 The first stacked unit 14 is formed. A second stack (18) of reflectors or mirrors is deposited on the active layer 16. The detailed structure of the first mirror stacking section 14, the active region 16 and the second mirror stacking section 18 was issued on July 23, 1991 and assigned to the same assignee as the present case. Included US Pat. No. 5,032,092 “Plasma Etching of Semi
Conductor Substrates ”.

Once the first mirror stack 14, active layer 16 and second mirror stack 18 are complete, the structure must be patterned to form one or more individual VCSELs. In this particular embodiment, patterning is performed as follows. Second mirror stacking section 18
A layer of photoresist material, either alone or in combination with an oxynitride material, is provided on the top surface of the substrate in any known manner. The photoresist layer is exposed and the material is removed to define the location and dimensions of trench 20. A trench 20 is then formed by etching the mirror stack 18 by ion milling or the etching process disclosed in the '092 patent shown above. In general, the trench 20 completely surrounds and defines the operating area or mesa 25. Mesa 2
5 has a generally circular cross section in this particular embodiment.

In this particular embodiment, trench 2
0 extends from the upper surface of the mirror laminated portion 18 to the inside thereof to a depth of about ½ of the size of the entire first mirror laminated portion 14. This depth is convenient for reasons that will become apparent below, but the trench 20 reduces the reflectivity of the mirror stack 18 in the volume between the bottom of the trench 20 and the active layer 16. It need only be deep enough to generate a non-laser illuminated volume below the trench 20. The non-laser illuminated volume surrounds the laser illuminated volume below the mesa 25, which is substantially coaxial with the mesa 25. In at least some applications, laser irradiation will not occur once the reflectivity drops below about 98%. A complete disclosure of the structure of laser 10 with mesas 25 is
Simultaneous application “Patterned Mirror Vertical Cavity Surface Emitti” filed on the same day as this case and assigned to the same assignee
ng Laser ”(patterned mirror vertical cavity surface emitting laser).

A trench 20 is formed to a desired depth, impurities or a doping material such as beryllium are deeply implanted into the second mirror laminated portion 18, and a buried implant is formed in the non-laser-irradiated volume of the second mirror laminated portion 18. Form the layer 27. Typically, a thick photoresist or silicon oxynitride layer 30
Are used as both a mask for etching the trench 20 and a mask for implanting impurities.
The impurities are selected to generate a conductivity type different from that of the second mirror stack 18. In the particular embodiment illustrated, the second mirror stack 18 has n-type conductivity and the injection layer 27 has p-type conductivity. Further, in this particular embodiment, beryllium is used as an impurity to achieve the deepest buried implant. This is because beryllium is the lightest and widely used impurity. However, it should be understood that any known implant material commonly used in the semiconductor industry can be used as implant 27. Also, because of the difficulty in implanting impurities to the desired depth, trench 20 may be formed deeper than would normally be required to obtain the desired reflectance reduction.
Thus, a buried pnpn structure is formed in the non-laser illuminated volume in the second mirror stack 18, which represents an inverted semiconductor junction and prevents current from flowing there.

The implant layer 27 substantially confines the current flow within the laser 10 to the laser irradiation volume beneath it, generally coaxial with the mesa 25. Also, the volume under the mesa 25 generally defines a volume of 10 lasers at which laser irradiation occurs due to the reduced reflectivity created by the trench 20. By controlling the current distribution to the desired laser irradiation volume only, the wasted current is minimized,
The efficiency of the laser 10 is maximized. Further, when the operating region is large, the threshold current increases, but the series resistance decreases and the output power further increases. Although it is useful to increase the depth of the trench 20 to obtain the desired depth of the implant layer 27, the implant layer 27 controls the current spread regardless of the depth of the trench 20.

In the manufacturing method of the present invention, the mode size for the lowest order mode is predetermined, and the diameter of the mesa 25 is set to be the same.
Masking the structure for etching the trench (or trenches) 20 is not critical, as the laser irradiation only occurs within the volume below and axially aligned with the mesa 25. Generally, the depth of the trench 20 is such that it does not contact the active layer 16, thereby improving reliability. Also, the width of the trench 20 is not critical and may be any convenient width depending on the application and the manufacturing steps below.

In FIG. 2, the mask layer 30 is removed after implantation and an optional layer 32 of Si implant is formed on the top surface of the laser 10 to prevent surface conversion. The laser 10 is then annealed to activate the implant and fill the buried implant layer 27.
To form. An n-type metal layer 34 is deposited on the surface of the laser 10 outside the mesa 25 and acts as a first electrical contact to apply a threshold current thereto. The p-type metal layer 36 is the substrate 12
Is attached to the back (lower) surface of the to function as a second electrical contact and applies a threshold current. Typically, the metal layers 34, 36 are made of nickel, germanium, gold and titanium, platinum, gold, respectively. The metal layers 34, 36 are made such that a geometric pattern is formed by using a common lift-off process. It should be appreciated that other masking structures and methods can be used to create geometric patterns of photoresist, dielectrics, etc.

FIG. 3 is a top emission VC incorporating the present invention.
It is sectional drawing of another Example of SEL50. Generally, V
The mirror laminated portion and the active portion of the CSEL 50 are the VC of FIG.
Constructed the same as the SEL 10, except that they are formed on the n-type substrate 52 and an implant layer 57 is implanted in the lower or first mirror stack 54, which is also an n-type material. That is. In this example, the implant layer 57 comprises p-type material. Since the second mirror stack 58 is a p-type material, the implant 57 forms a pnpn junction to prevent current flow therethrough, thereby allowing the current to be below the mesa 55 and generally coaxial therewith. Pour into irradiated volume. From this example, it can be seen that a variety of different types of conductivity type materials can be utilized to form a VCSEL. The only requirement is that the implant layer be positioned so that current does not flow into the laser-irradiated volume and diffuse into the non-laser-irradiated portion of the VCSEL.

To form the top electrical contact of the VCSEL 50, a transparent metal p-type contact material is deposited on the top surface of the mesa 55 to form a first electrical contact. A typical metal used as a transparent metal is indium tin oxide (IT).
O). Since layer 60 is optically transparent, it can be deposited directly on the light emitting area (mesa 55) and does not interfere with light emission. The second metal layer 64, which in this example is an n-type material, is deposited on the back (lower) surface of the substrate 52 to form a second electrical contact. Another advantage of this particular structure is that
The mesas 55 help to limit the current to the laser illuminated volume indicated by the solid arrow 62. Deeper etching of the mesas and deposition of an insulating layer on the outside of the mesas helps to limit the current. In this way VCSEL50
Includes a dual current limiting structure, a mesa 55 and an implant layer 57.

Thus, a novel and improved top-emission VCSEL is disclosed that is simple to manufacture due to the self-alignment of mirror etch and impurity implantation, and the virtually self-aligned metallization. Furthermore, the power output and efficiency of the laser are maximized due to the optical mode control performed by the trench and the current distribution control performed by the impurity implantation. Finally, although the discussion of making a single laser is discussed here,
It should be understood that individual lasers, arrays of lasers, semiconductor wafers of lasers, etc. can be readily manufactured by the disclosed method.

[Brief description of drawings]

FIG. 1 is a simplified, cross-sectional view of the middle of a top emitting VCSEL incorporating the present invention.

FIG. 2 is a view similar to FIG. 1 of the completed structure.

FIG. 3 is a cross-sectional view of another embodiment of a top emitting VCSEL incorporating the present invention.

[Explanation of symbols]

 10 Laser 12 Substrate 14, 18 Mirror Stack 20 Trench 25 Emission Area 27 Impurity Implant Layer 30 Mask Layer

Claims (3)

[Claims] 1. A method of making a top emitting VCSEL comprising first (14) and second (18) mirror stacks deposited on each side of an active layer (16), the method comprising:
Defining an emission area (25) in the mirror stack (18); etching the second mirror stack (18) to form a trench (20) surrounding the emission area (25), Region (20) and said active layer (16)
Extending the depth of the trench (20) to sufficiently lower the reflectivity below the amount required to effect laser irradiation within the non-laser irradiated volume of the laser (10) between and. Impurities (27, 57) are implanted into the non-laser-irradiated volume of either one of the first (14) and second (18) mirror laminated portions to form the implants. An implant volume (27, 57) having a conductivity type different than one of the stacks is formed to define an implant volume (27, 57) that is generally axially aligned with the emission region. 57) to form 57). 2. A method of making a top emitting VCSEL comprising: providing a substrate (12) having first and second opposing major surfaces; on the first major surface of the substrate (12). Depositing a first mirror stack (14); depositing an active layer (16) on the first mirror stack (14); second mirror stack (18) on the active layer (16) Attaching the second mirror stacking portion (1
8) defining an emission region (25) within the second mirror stack (18) to form a trench (20) surrounding the emission region (25), and the trench region (20). The depth of the trench (20) in order to reduce the reflectivity sufficiently below the amount required for laser irradiation within the non-laser irradiated volume of the laser (10) between the active layer (16) and the active layer (16). The length of the first and second mirror laminated portions, and impurities (27, 57) are injected into the non-laser-irradiated volume of either one of the first and second mirror laminated portions to form the first and second implants. Forming an implant volume having a conductivity type different from that of one of the second stacks to form the implant volume to define a generally axially aligned laser irradiation volume in the emitting region (25). Stage; Wherein the. 3. A top-emission VCSEL comprising: an active layer (16) having opposing major surfaces; a first mirror stack (14) on one major surface of the active layer; the active layer (1).
Second mirror stack (18) on the other major surface of 6)
And the second mirror stacking part (18) is
From the main surface of the mirror stacking part (18) to the active layer (16)
Has an emission region (25) defined by a trench (20) extending toward, the trench (20) surrounding the emission region (25) and extending to a sufficient depth to provide the trench (20). 20) and the second mirror stack (1) which reduces the reflectivity below the amount required for laser irradiation within the non-laser irradiated volume of the laser between said active layer (16).
8); and the impurity implants (27, 5) in one of the first (14) and second (18) mirror stacks.
7), wherein the implant is the implant (27,5)
7) formed with the first (14) and second (18)
Forming an implant volume having a conductivity type different from one conductivity type of the stack, the implant volume being the emission region (25).
And a top-emission VCSE characterized by an impurity implant (27, 57) formed to define a current path (62) generally axially aligned therewith.
L.